Control means for controlling static gas pressures in support means for a reflector of an optical telescope



Oct. 27, 1964 D. E. WALLIS 3,154,627

CONTROL MEANS FOR CONTROLLING STATIC GAS PRESSURES IN SUPPORT MEANS FORA REFLECTOR OF AN OPTICAL TELESCOPE Filed'Aug. 8, 1.961 2 Sheets-Sheet 1Filed Aug. 8, 1961 Oct. 27, 1964 D. E. WALLIS ,1 27

CONTROL MEANS FOR CONTROLLING STATIC GAS PRESSURES IN SUPPORT MEANS FORA REFLECTOR OF AN OPTICAL. TELESCOPE 2 Sheets-Sheet 2 United StatesPatent 3,154,627 CONTROL MEANS FOR CONTROLLING STA'IEC GAS PRESSURES 1NSUPPQRT MEAN FOR A REFLECTUR OF AN UP'IICAL TELESQGRE Douglas E. Wallis,Newcastle-upon-Tyne, Engiand, as-

signor to Sir Howard Grubh Parsons & Company Linn ited,NeWcastle-upon-Tyne, England Filed Aug. 8, 1961, Ser. No. 130,120(Jlaims priority, application Great Britain Aug. 9, 1960 8 Claims. ((31.88-32) This invention relates to control means for controlling staticgas pressures.

One application of such control means is in optical reflectingtelescopes where the reflector or mirror may be supported on the sideremote from the reflecting surface, by an air bag or by a larger numberof individual supports each operated by static air pressure. The purposeof such support is to prevent or reduce warping of the reflector.

It is important in such cases that the static air pressure in the airbag or in the individual supports should be maintained constant when thetelescope is in a given position, the actual value at which it remainsconstant depending on the attitude of the mirror.

The object of the present invention is to provide control means forachieving this.

It is a further object of the present invention to provide improvedcontrol means for controlling static gas pressure in a container.

The foregoing and further objects and advantages of the invention willbe made more apparent as the specification proceeds.

The invention will be further described, by way of example, withreference to the drawings in which:

FIGURE 1 shows a section through a control device in accordance with oneembodiment of the invention suitable for controlling the pressure of astatic air supply to an air bag or bags supporting the reflector of anoptical telescope;

FIGURE 2 is a section on line IIII of FIGURE 1; and

FIGURE 3 is a schematic arrangement showing the application of thecontrol device of FIGURE 1 to the control of pressure in air bagssupporting the reflector of an optical telescope.

In carrying the invention into effect in the form illustrated by way ofexample and referring to FIGURE 1, a control device consists of a casing1 closed by an end wall 1a at one end and open to atmosphere at theother. Located in the casing 1 is a piston 2, an annular space beingleft between the piston and the casing. Air is directed into saidannular space to keep the piston in spaced relation to the casing sothat the piston effectively floats within the casing on a film of air.Air is passed under pressure into the casing between the piston and thecasing wall through jets 3. The air for the jets 3 is supplied from amanifold 4 surrounding the casing 1 for part of its length. The manifoldis fed with air through inlet connection 5.

The jets 3 are disposed in a plane at right angles to the axis of thecasing 1 and may be disposed at an angle to the radial direction asshown in FIGURE 2 so as to produce a rotational component on the pistonto cause it to rotate. Air passing through jets 3 flows out toatmosphere at the open end of the cylinder and through passages 6. Thepiston 2 is recessed opposite the passages 6 so as to provide an anularrecess 6a in which the air can collect prior to passing through passages6.

Beyond the passages 6 in the direction of the closed end of the cylinderthe piston carries a further annular recess 7 which provides an inletannulus for air which is connected to the air bag through the casing.The axial length of the further recess 7 is such that for the full rangeof movement of the piston, an inlet 8 for the air supply to the air bagis in communication with the recess '7 The position of the piston shownin the drawing approximates to the maximum travel of the piston awayfrom the end wall 1a of the casing 1.

Air entering the further recess 7 passes to a space 9 between the end ofthe piston and wall in through passages in the piston formed by axialjets 10 which act as stabilising jets to reduce fluctuation in thepiston movement. Space 9 is in communication with the air bag throughmain outlet connection 11.

There is a leakage path for the air from space 9 to an outlet 12 in thecasing 1, a variable restriction in this leakage path being formed by aland 13 on the piston, the wall of the casing and the outlet 12 in orderthat the pressure in space 9 and hence in the airbag can be keptconstant. It will be seen that the length of the restriction isdependent on the position of the piston.

Another land 14 on the piston provides an escape path of constant axiallength between the piston and casing 1 from recess 7 to outlet 12irrespective of the position of the piston. Another land 16 on thepiston forms in conjunction with the casing a restriction of constantlength between opening 6 and recess 7. This restriction prevents anysubstantial flow beyond opening 6 towards recess 7 or in the reversedirection. This restriction is of constant length irrespective of theposition of the piston.

The device can be orientated through an angle from the vertical positionso that the pressure in space 9 is a function of the angle of thepiston. In the vertical position the total weight acts and when at anangle to the vertical a component of the weight acts.

The static pressure in the air bag can thus be varied by turning thedevice through an angle. The device is mounted so that its longitudinalaxis is parallel to the optical axis of the mirror. Then if the deviceis moved in synchronism with the mirror the device provides the desiredsupporting pressure for any attitude of the mirror.

Referring to FIGURE 3 a reflector 17 of an optical telescope is mountedin a housing 18. The reflector is supported in the housing by annularair bags 19. It is also supported laterally along its sides by members20. The reflector is tilted by tilting the housing 18.

Control devices of the form illustrated in FIGURE 1 are indicated at 21and these are mounted on the housing 18 so that as the reflector tiltsthey tilt in synchronism therewith. It is not, however, essential thatthey be mounted on housing 18 provided they can be caused to move insynchronism with movements of the reflector.

Air from a compressor 22 passes via conduit 23 to a receiver 24 throughdriers 25, and filter 26. After filter 26 the conduit 23 divides intotwo separate conduits 23a, 23b. Both conduits contain valves 27,pressure regulators 28 and pressure gauges 29. Conduit 23a passes toinlet manifolds 4 of each control device whilst conduit 23b passes toinlets 8 of the respective control devices.

Air from outlets 11 of the respective control devices passes throughconduits 30, 31, 32 to the air bags 19.

With a reflector of the shape shown the static air pressure in the outerbag would be higher than that in the inner bag as it has a greaterthickness of material to support.

In the form illustrated the piston is made in two parts 211, 2b ofdiflerent density materials so that the resultant density of the pistoncan be varied more conveniently. The length of the piston can also bevaried more easily. The device is highly accurate because of thefloating piston and the fact that the escape paths for air from q) thecasing are of constant length for all positions of the piston and can beused to control the static air pressure to within i A mm. of Waterirrespective of wide variations of the air supply to the controller.

In one typical embodiment the piston is 1 /2 diameter and has part 2a ofaluminium and part 2b of mild steel. The casing is of mild steel and 4%"long. The jets 3 are formed in two separate rings each containing 6 jetsof 0.03" dia. The clearance between the piston and casing and hence thethickness of the air film is 0.001". There are 12 outlet holes 6 each0.125 dia. and there are 12 outlet ducts 0.125 dia. The stationary jetsare six in number and are 0.03 dia. The pressure of the air introducedto manifold 4 is 20 lb./in. and that to inlet 8 is lb./in.approximately. The static pressure in the air bag is 0.91 lb./in. whenthe axis of the cylinder is vertical.

Whilst the invention has been described using air, gases other than aircan be used.

Further, whilst the invention has been described in connection with themaintenance of a constant static air pressure in an air bag for areflecting telescope it can be used in any circumstances where it isnecessary to maintain a sensibly constant static air pressure in one ormore containers. In addition or alternatively it can be used to apply asensibly constant force to a body.

In certain circumstances there may be a tendency for the piston tooscillate depending on the nature of and the volume of the air containerand the connecting means. In such circumstances the oscillations may bedamped by connecting space 9 to a further chamber through a restrictionor orifice.

A baffle may be fitted to the end of the piston to counteract anyreaction on the piston due to the impact of air on the end wall 1a. Thebattles direct the air in a radial direction.

I claim:

1. Means for controlling static gas pressure in a container which meanscomprise a casing closed at one end by an end wall and open toatmosphere at the other, a piston located in the casing defining anannular space between the piston and the wall of the casing, meansincluding openings disposed in opposition to one another around thecasing wall for directing gas, through the said wall to said annularspace, in a plane perpendicular to the axis of the casing to maintainthe piston in spaced relation to the casing wall for all attitudes ofthe casing, egress passages for said gas in the casing wall locatedbetween the said openings and the end wall of the casing, an inlet forgas whose pressure is to be controlled located in the casing wallbetween the egress passages and the end wall of the casing, a mainoutlet for said gas connected to a space between the piston and the endwall of the casing, said outlet being connected to the container,passages in the piston for permitting continuous flow of gas from theinlet to the said space and a variable restriction for bleeding gas fromsaid space to atmosphere, which variable restriction is formed between aland on the piston, the casing wall and a further outlet located betweenthe inlet and the said space, movement of the piston varying the openingof said further outlet.

2. An optical telescope comprising a reflector, a housing therefor andinflatable containers located between the reflector and the housing,control means for maintaining a pre-determined static gas pressure insaid containers, mounted on said housing so as to be tiltable with thereflector, means connecting the control means to a container and meanssupplying gas to said container, said control means comprising a casingclosed at one end and open to atmosphere at the other, a piston locatedin the casing defining an annular space between the piston and the wallof the casing, means, including openings disposed in opposition to oneanother around the casing wall, for directing gas through the wall ofthe easing into said annular space in a plane perpendicular to the axisof the casing to maintain the piston in spaced relation to the wall ofthe casing for all attitudes of the reflector, egress passages for saidgas in the said casing wall located between said openings and the endwall of the casing, an inlet for gas to be supplied to the containerlocated in the casing wall between said egress passages and the end wallof the casing, a main outlet for said gas connected to a space betweenthe piston and the end wall of the casing, said outlet being connectedto the container, passages in the piston for permitting continuous flowof gas from said inlet to the said space and a variable restriction forbleeding gas from said space to atmosphere, said variable restrictionbeing formed between a land on the piston, the wall of the casing and afurther outlet located between the inlet and the space between the endof the piston and the end wall of the casing, movement of the pistonvarying the opening of said further outlet.

3. Control means as claimed in claim 1, in which the means for directinggas through the wall of the casing and into annular space between thepiston and the casing comprise an inlet manifold for gas under pressure,said manifold surrounding the casing for a portion of its axial length,and jets disposed in opposition to one another around the wall of thecasing communicating with the manifold and with said annular space.

4. Control means as claimed in claim 1 in which the means for conductinggas through the annular space between piston and casing comprise aninlet manifold for gas under pressure, said manifold surrounding thecasing for a portion of its axial length, and jets disposed inopposition to one another around the Wall of the casing communicatingwith said manifold and with said annular space, said jets lying in aplane at right angles to the axis of the casing but at an angle to theradial direction to produce a rotational component acting on the pistonto cause it to rotate.

5. Control means as claimed in claim 1 in which the piston has anannular recess facing, in all positions of the piston, the inlet for gassupplied to the container and the passages for the gas through thepiston from said recess to the space between the end of the piston andthe end wall of the casing is formed by axially directed jets in thepiston.

6. Control means as claimed in claim 1 in which a further land isprovided on the part of the piston between the land forming part of thevariable restriction and the inlet for gas supplied to the containerwhich further land provides in conjunction with the wall of the casing arestriction of constant axial length for any gas leaking between thesaid inlet and the variable restriction.

7. Control means as claimed in claim 1 in which a land is provided onthe part of the piston lying between the inlet for gas supplied to thecontainer and the egress passages in the casing for egress of gasconducted through the annular space between piston and casing, said landin conjunction with the wall of the casing forming a restriction ofconstant axial length for any gas leaking between said inlet and saidpassages.

8. Control means as claimed in claim 1 in which baflie means are fittedto the end of the piston opposite the end wall of the casing to deflectin a radial direction gas entering the space at the end of the pistonfrom the passages in the piston.

References Cited in the file of this patent UNITED STATES PATENTS1,734,284 Blair Nov. 5, 1929 1,966,841 Zelov July 17, 1934 2,750,952Best June 19, 1956 2,918,072 Boler Dec. 22, 1959 2,940,463 Balfour June14, 1960 2,956,761 Weber Oct. 18, 1960 FOREIGN PATENTS 987,988 FranceApr. 25, 1951

2. AN OPTICAL TELESCOPE COMPRISING A REFLECTOR, A HOUSING THEREFOR ANDINFLATABLE CONTAINERS LOCATED BETWEEN THE REFLECTOR AND THE HOUSING,CONTROL MEANS FOR MAINTAINING A PRE-DETERMINED STATIC GAS PRESSURE INSAID CONTAINERS, MOUNTED ON SAID HOUSING SO AS TO BE TILTABLE WITH THEREFLECTOR, MEANS CONNECTING THE CONTROL MEANS TO A CONTAINER AND MEANSSUPPLYING GAS TO SAID CONTAINER, SAID CONTROL MEANS COMPRISING A CASINGCLOSED AT ONE END AND OPEN TO ATMOSPHERE AT THE OTHER, A PISTON LOCATEDIN THE CASING DEFINING AN ANNULAR SPACE BETWEEN THE PISTON AND THE WALLOF THE CASING, MEANS, INCLUDING OPENINGS DISPOSED IN OPPOSITION TO ONEANOTHER AROUND THE CASING WALL, FOR DIRECTING GAS THROUGH THE WALL OFTHE CASING INTO SAID ANNULAR SPACE IN A PLANE PERPENDICULAR TO THE AXISOF THE CASING TO MAINTAIN THE PISTON IN SPACED RELATION TO THE WALL OFTHE CASING FOR ALL ATTITUDES OF THE REFLECTOR, EGRESS PASSAGES FOR SAIDGAS IN THE SAID CASING WALL LOCATED BETWEEN SAID OPENINGS AND THE ENDWALL OF THE CASING, AN INLET FOR GAS TO BE SUPPLIED TO THE CONTAINERLOCATED IN THE CASING WALL BETWEEN SAID EGRESS PASSAGES AND THE END WALLOF THE CASING, A MAIN OUTLET FOR SAID GAS CONNECTED TO A SPACE BETWEENTHE PISTON AND THE END WALL OF THE CASING, SAID OUTLET BEING CONNECTEDTO THE CONTAINER, PASSAGES IN THE PISTON FOR PERMITTING CONTINUOUS FLOWOF GAS FROM SAID INLET TO THE SAID SPACE AND A VARIABLE RESTRICTION FORBLEEDING GAS FROM SAID SPACE TO ATMOSPHERE, SAID VARIABLE RESTRICTIONBEING FORMED BETWEEN A LAND ON THE PISTON, THE WALL OF THE CASING AND AFURTHER OUTLET LOCATED BETWEEN THE INLET AND THE SAPCE BETWEEN THE ENDOF THE PISTON AND THE END WALL OF THE CASING, MOVEMENT OF THE PISTONVARYING THE OPENING OF SAID FURTHER OUTLET.